H C Gerhardt

• PhD
• Professor Emeritus at University of Missouri

From prehistoric times, humans have certainly been aware of the existence of sounds of frogs and toads. The significance of sounds for mating was noted by Aristotle (Historia Animalium, translated as History of Animals by D’Arcy Wenthworth Thompson Clarendon Press, Oxford, 400 BCE). However, the understanding of the nature of sound and of its trans...

After polyploid species are formed, interactions between diploid and polyploid lineages may generate additional diversity in novel cytotypes and phenotypes. In anurans, mate choice by acoustic communication is the primary method by which individuals identify their own species and assess suitable mates. As such, the evolution of acoustic signals is...

After polyploid species are formed, interactions between diploid and polyploid lineages may generate additional diversity in novel cytotypes and phenotypes. In anurans, mate choice by acoustic communication is the primary method by which individuals identify their own species and assess suitable mates. As such, the evolution of acoustic signals is...

Albert Feng pioneered the study of neuroethology of sound localization in anurans by combining behavioral experiments on phonotaxis with detailed investigations of neural processing of sound direction from the periphery to the central nervous system. The main advantage of these studies is that many species of female frogs readily perform phonotaxis...

Significant variation in genome size occurs among anuran amphibians and can affect cell size and number. In the gray treefrog complex in North America increases in cell size in autotriploids of the diploid (Hyla chrysoscelis) altered the temporal structure of mate-attracting vocalizations and auditory selectivity for these properties. Here we show...

Polyploid speciation has played an important role in evolutionary history across the tree of life, yet there remain large gaps in our understanding of how polyploid species form and persist. While systematic studies have been conducted in numerous polyploid complexes, recent advances in sequencing technology have demonstrated that conclusions from...

Polyploid speciation has played an important role in evolutionary history across the tree of life, yet there remain large gaps in our understanding of how polyploid species form and persist. While systematic studies have been conducted in numerous polyploid complexes, recent advances in sequencing technology have demonstrated that conclusions from...

Female preferences for males producing their calls just ahead of their neighbours, leader preferences, are common in acoustically communicating insects and anurans. While these preferences have been well studied, their evolutionary origins remain unclear. We tested whether females gain a fitness benefit by mating with leading males in Neoconocephal...

Sustained perfect synchrony of signal production by animals is unrealistic, but even near-synchronous signalling is extremely rare. Near-synchronous signalling has been documented in some orthopteran insects and fireflies, and one kind of frog. This study provides observations and analyses of sustained bouts of impressive near-synchronous calling b...

Speciation by polyploidy—duplication of chromosome sets—commonly occurs in plants and happened twice in the early evolutionary history of vertebrates. The gray treefrog (Hyla versicolor) is a recently evolved tetraploid species found in the eastern United States, where it often occurs with a cryptic diploid species (Hyla chrysoscelis). Assortative...

In his book Descent of Man and Selection in Relation to Sex, Darwin (1) made a compelling argument that evolution could not be explained solely on the basis of differential survival (natural selection). In particular, traits that enhance an individual’s reproductive success (sexual selection) often decrease its chances of survival. For example, the...

Interspecific aggression has important consequences for ecological processes and the evolution of behavioral strategies. We examined interspecific aggressive interactions in the 2 gray tree frog species, Hyla chrysoscelis and Hyla versicolor. These species call side by side in the same ponds, and acoustic interference occurs because of the similar...

Detection of genetic and behavioral diversity within morphologically similar species has led to the discovery of cryptic species complexes. We tested the hypothesis that the canyon treefrog (Hyla arenicolor) may consist of cryptic species by examining mate-attraction signals among highly divergent lineages defined by mitochondrial DNA (mtDNA). Unex...

Genetic variation in sexual displays is crucial for an evolutionary response to sexual selection, but can be eroded by strong selection. Identifying the magnitude and sources of additive genetic variance underlying sexually-selected traits is thus an important issue in evolutionary biology. We conducted a quantitative genetics experiment with gray...

Ethologists have often reported preferences for novel signals, especially if they are more extravagant than normal signals. Such preferences presumably reflect sensory biases that may promote the evolution of both novel and complex signals. We tested behavioural responses of female grey treefrogs, Hyla versicolor, to novel complex calls in relation...

Background: Reproductive character displacement is a geographical pattern in which mateattracting signals, preferences or both differ more in areas of sympatry than in areas of allopatry. Questions: What selective forces drive reproductive character displacement? What are its consequences? Methods: Reproductive character displacement in mate-attrac...

As animal contests escalate, variation in the performance of aggressive signaling behaviors can give important insights into contest dynamics. In anuran amphibians, males of numerous species utilize distinctive aggressive vocalizations during disputes over calling spaces. Little is known, however, about the causes and consequences of variation in a...

Call timing is an important component of the behavioral repertoire of many chorusing species that compete acoustically for mates. The costs and benefits of particular call-timing patterns may vary with factors in the social environment, yet few studies have examined the possibility of socially mediated plasticity in call timing. We studied the effe...

In many species of anurans, advertisement calls excite only one of the two inner-ear organs. One prediction of the pre-existing bias hypothesis is that signal innovations that additionally excite the "untapped" organ will be more behaviorally effective than normal calls. However, recent studies have shown that females of three species with single-p...

Abstract Performance limitations on signal production constrain signal evolution. Variation in signaling performance may be related to signaler quality and therefore is likely to be a salient aspect of communication systems. When multiple signal components are involved in communication, there may be trade-offs between components, and performance ca...

We surveyed the geographical variation in male advertisement calls of the wide‐ranging canyon treefrog, Hyla arenicolor, and found large call differences among geographically distant lineages that had been characterized by a recent phylogeographical study. To test whether these call differences were biologically relevant and could allow reproductiv...

Background/Question/Methods Aggressive behavior has been studied intensively in animals because the factors involved in success in aggressive interactions may be major component of individual fitness. An individuals’ past experience could affect its behavior in future aggressive interactions. One particularly notable effect of previous experience...

Aggressive interactions in animals are often resolved in favour of the individual with superior fighting ability, or resource-holding potential (RHP). A recent revival of studies of aggressive behaviour has focused on the assessment strategies used in animal contests. Strategies of dispute resolution through mutual or self-assessment of RHP differ...

For polyploid species to persist, they must be reproductively isolated from their diploid parental species, which coexist at the same time and place at least initially. In a complex of biparentally reproducing tetraploid and diploid tree frogs in North America, selective phonotaxis--mediated by differences in the pulse-repetition (pulse rate) of th...

Detection of genetic and behavioural diversity within morphologically similar species has led to the discovery of cryptic species complexes. We tested the hypothesis that US populations of the canyon treefrog (Hyla arenicolor) may consist of cryptic species by examining mate-attraction signals among three divergent clades defined by mtDNA. Using a...

The temporal relationship between signals often has strong and repeatable influences on receiver behaviour. While several studies have shown that receivers prefer temporally leading signals, we show that the relative timing of signal elements within overlapping signals can also have repeatable influences on receiver responses. Female grey treefrogs...

Signal design is influenced by multiple sources of selection in the form of conspecific receivers, other species that signal at the same time and place, predators, and the physical environment. Chemical signals are designed for relatively rapid short-duration messages (alarm) or more durable markers of territorial boundaries by changes in molecular...

Even simple biological signals vary in several measurable dimensions. Understanding their evolution requires, therefore, a multivariate understanding of selection, including how different properties interact to determine the effectiveness of the signal. We combined experimental manipulation with multivariate selection analysis to assess female mate...

Senders and receivers influence dynamic characteristics of the signals used for mate attraction over different time scales. On a moment-to-moment basis, interactions among senders competing for a mate influence dynamic characteristics, whereas the preferences of receivers of the opposite gender exert an influence over evolutionary time. We observed...

Sound file of average call of a male H. avivoca calling in a chorus. The call consist of 24 pulses of about 0.050 ms given at intervals of about 0.075 ms for a total call length of 3 s. Uninterrupted calls have a constant pulse rate of about 8.4 pulses per second at a temperature of about 24°C (see Fig. 1a and text)

Stereo sound file of an advertisement-call interaction between two neighboring males. The first call, produced by male 1, is 2.34 s long and contains 18 pulses; the next call of male 1 is 2.46 s long and contains 17 pulses. The call is completely overlapped by the call of male 2, which is 3.17 s long and contains 24 pulses. During call overlap, bot...

Hormonal levels fluctuate during the breeding season in many anurans, but the identity of the hormones that modulate breeding behavior and their effects remain unclear. We tested the influence of a combined treatment of progesterone and prostaglandin on phonotaxis, the key proceptive reproductive behavior of female anurans. First, we found that fem...

The two main spectral components of the advertisement calls of two species of North American gray treefrogs (Hyla chrysoscelis and H. versicolor) overlap broadly in frequency, and the frequency of each component matches the sensitivity of one of the two different auditory inner ear organs. The calls of the two species differ in the shape and repeti...

To understand the variation in aggressiveness and factors important for contest outcome, we quantified and compared agonistic interactions of four field cricket species in eastern North America: Gryllus fultoni (Orthoptera; Gryllidae), G. vernalis, G. pennsylvanicus, and G. rubens. The most aggressive behavior that we observed, the grapple, was fre...

Frogs have two inner ear organs, each tuned to a different range of frequencies. Female treefrogs (Hylidae) of three species in which males produce calls with a bimodal spectrum (Hyla chrysoscelis, H. versicolor, H. arenicolor) preferred alternatives with a bimodal spectrum to alternatives with a single high-frequency peak. By contrast, females of...

Signal-timing adjustment is common in communally signaling species, and there is large variation in signal-timing formats found in nature. We conducted a survey of geographic variation in female signal-timing preferences and male signaling behavior of a tree frog to test predictions of two hypotheses about the sources of selection acting on signal-...

The evolution of complex signals may be favoured by hidden preferences or pre-existing sensory biases. Females of two species of grey treefrogs (Hyla chrysoscelis and Hyla versicolor) were tested with combinations of a conspecific advertisement call and acoustic appendages. Appendages consisted of aggressive calls and segments of advertisement call...

Two closely related wood-cricket species, Gryllus fultoni (Orthoptera: Gryllidae) and G. vernalis, produce similar calling songs, consisting of 3-pulse chirps. Analysis of field and laboratory recordings of calling songs showed that, after correction to a common temperature, there was a divergence in chirp and pulse rates between far allopatric pop...

Two species of closely related wood crickets, Gryllus vernalis (Orthoptera: Gryllidae) and G. fultoni, occur together in the eastern USA and have a similar calling-song structure, consisting of three-pulse chirps. Previous studies revealed that male calling song and female selectivity were divergent between sympatric and far allopatric populations...

H Carl Gerhardt was born in Newport News, Virginia, on May 23, 1945. He grew up in Savannah, Georgia, and in 1966 received a B.S. degree in zoology from the University of Georgia. He received M.A. (1968) and Ph.D. (1970) degrees from the University of Texas at Austin. From early 1970 to mid-1971, he was a postdoctoral scholar at Cornell University,...

We studied the advertisement signals in two clades of North American hylid frogs in order to characterize the relationships between signal acoustic structure and underlying behavior. A mismatch was found between the acoustic structure and the mechanism of sound production. Two separate sets of phylogenetic characters were coded following acoustic v...

We investigated the effects of overlap between the advertisement calls of two closely related and often-sympatric species of grey treefrogs on female phonotactic behaviour and signal selectivity. The tetraploid H. versicolor and the diploid H. chrysoscelis have advertisement calls consisting of trains of stereotyped pulses that are similar in their...

Two species of closely related wood cricket, Gryllus fultoni (Orthoptera: Gryllidae) and Gryllus vernalis, occur together in some parts of the eastern United States and have a similar calling song structure, consisting of three-pulse chirps. A previous study revealed that chirp rate in G. fultoni was highest (greatest difference vis--vis chirp rate...

Polyploidization is one of the few mechanisms that can produce instantaneous speciation. Multiple origins of tetraploid lineages from the same two diploid progenitors are common, but here we report the first known instance of a single tetraploid species that originated repeatedly from at least three diploid ancestors. Parallel evolution of advertis...

In the eastern United States the wood cricket Gryllus fultoni (Orthoptera: Gryllidae) occurs in sympatry with G. vernalis in an area between eastern Kansas and west of the Appalachian Mountains. Calling songs were recorded from 13 sympatric and allopatric localities. Both field and laboratory recordings showed that chirp rate (CR) and pulse rate (P...

Advertisement calls of green treefrogs (Hyla cinerea) have two spectral peaks centered at about 1 kHz and 3 kHz. Addition of a component of intermediate frequency (1.8 kHz) to a synthetic call reduced its attractiveness to females relative to an alternative lacking this component. This mid-frequency suppression occurred over a 20-dB range of playba...

Females are expected to use spectral properties of acoustic signals for mate choice because dominant frequency often provides reliable information about male size. The advertisement calls of grey treefrogs (Hyla chrysoscelis and H. versicolor) have two main frequency bands: the amplitude of the dominant, high-frequency band averages 7–10 dB greater...

Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. Two-alte...

In addition to spectral call components, temporal patterns in the advertisement-call envelope of green treefrog males ( Hyla cinerea) provide important cues for female mate choice. Rapid amplitude modulation (AM) with rates of 250-300 Hz is typical for this species' advertisement calls. Here we report data on the encoding of these rapid call modula...

We investigated the effects of dopamine depletion on acoustically guided behavior of anurans by conducting phonotaxis experiments with female gray treefrogs (Hyla versicolor) before and 90 min after bilateral injections of 3, 6, or 12 microg 6-hydroxydopamine (6-OHDA) into the telencephalic ventricles. In experiments with one loudspeaker playing ba...

The most commonly heard vocalizations of frogs are advertisement calls, which attract gravid females and mediate aggressive interactions between males. Frog vocalizations are energetically costly to produce, and body size often constrains the dominant frequency and intensity of vocalizations; propagation and degradation of these signals are affecte...

Diencephalic and midbrain auditory nuclei are involved in the processing of auditory communication signals in anurans [Comparative Hearing: Fish and Amphibians, Springer-Verlag, New York, 1999, p. 218], but their exact roles in acoustically guided behavior, such as female phonotaxis, are unclear. To address this question, behavioral experiments wer...

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Walk near woods or water on any spring or summer night and you will hear a bewildering (and sometimes deafening) chorus of frog, toad, and insect calls. How are these calls produced? What messages are encoded within the sounds, and how do their intended recipients receive and decode these signals? How does acoustic communication affect and reflect...

Interactions between species can affect the evolution of their sexual signals, receiver selectivity, or both. One commonly expected outcome is reproductive character displacement, whereby adverse consequences of mismating select for greater differentiation of communication systems in areas of sympatry than in areas of allopatry. We found evidence o...

We assembled groups of up to eight male gray treefrogs, Hyla versicolor, in an artificial pond and examined vocal behavior under conditions of different chorus size. Males avoided call overlap when calling in groups of two, but not in larger choruses. The pattern of interference failed to reveal selective attention based on inter-male separation, a...

Female anurans typically show strong phonotactic selectivity for synthetic signals having pulse‐repetition (pulse) rates that are close to those in advertisement calls produced by conspecific males. Auditory neurons showing temporal selectivity for species‐typical pulse rates (especially bandpass neurons) are commonly reported from the inferior col...

Some territorial animals display low levels of aggression towards a familiar territorial neighbour in its usual territory, but exhibit high levels of aggression towards neighbours in novel locations and unfamiliar individuals. Here, we report results from a field playback study that investigated whether territorial males of the North American bullf...

Despite intense interest in mate choice, relatively little is known about how individuals sample prospective mates. Indeed, a key issue is whether females sample males or simply mate with the first male encountered. We investigated mate sampling by female barking treefrogs (Hyla gratiosa). Females choosing mates in natural choruses did not move bet...

Studies of mate attraction have traditionally employed one of two experimental methods: choice tests in which female preferences from among two or more signals are tabulated, or single-stimulus tests in which the female response to one signal is quantified. Choice tests have long been preferred for examining mate attraction in anurans. Inspired by...

Studies of vocal behavior in anurans provide significant insights about the mechanisms and evolution of animal communication. Females extract the information required for a mating decision from relatively stereotyped advertisement calls that are produced by males. Aggressive signals, used in exchanges between males, are more variable in form, as mi...

Some territorial animals discriminate among neighbours and strangers based on individual differences in acoustic signals. Male North American bullfrogs, Rana catesbeiana, display this form of discrimination based on individual variation in advertisement calls. In this study, we investigated the acoustic basis of neighbour–stranger discrimination to...

Territorial animals often exhibit relatively lower levels of aggression toward familiar territorial neighbors than toward strangers. Habituation to a neighbor or its communication signals has been proposed to account for this reduced aggression between adjacent territorial neighbors. The authors asked whether discrimination between neighbors and st...

Whole-genome duplication is believed to have played a significant role in the early evolution and diversification of vertebrate animals. The establishment of newly arisen polyploid lineages of sexually reproducing animals requires assortative mating between polyploids. Here, we show that genome duplication can directly alter a phenotypic trait medi...

Territorial animals often exhibit relatively lower levels of aggression toward familiar territorial neighbors than toward strangers. Habituation to a neighbor or its communication signals has been proposed to account for this reduced aggression between adjacent territorial neighbors. The authors asked whether discrimination between neighbors and st...

We studied female mate choice by Hyla versicolor in three venues to examine how acoustic and spatial complexity, background noise, and the calling behavior of males might influence preferences manifest in previous laboratory two-stimulus choice tests. Our laboratory-based two-stimulus choice tests with and without broadcasts of chorus noise demonst...

Individuals of many territorial species discriminate between familiar territorial neighbors and unfamiliar strangers based on individual differences in acoustic signals. Many anuran amphibians are territorial and use primarily acoustic communication during social interactions, but evidence for acoustically mediated individual discrimination is avai...

Preference functions, which quantify preference strength relative to variation in male traits or signals, are central to understand- ing mechanisms and consequences of female choice. Female tree frogs (Hyla versicolor) choose mates on the basis of advertise- ment calls and prefer long calls to short calls. Here we show, in two experimental designs,...

Males of the quacking frog Crinia georgiana produce calls consisting of 1–11 notes. Playback experiments using synthetic calls showed that males tend to match the number of notes in 2-note and 4-note stimuli; however, males tended to produce more than 1 note in response to a 1-note stimulus and fewer than 8 notes in response to an 8-note stimulus....

A mating preference function describes the relationship between variation in a trait in potential mates and the strength of the preference for that trait. Few studies have measured mating preference functions either at a population level or for individuals. We used two-choice playback experiments to determine the mating preference functions of indi...

— A mating preference function describes the relationship between variation in a trait in potential mates and the strength of the preference for that trait. Few studies have measured mating preference functions either at a population level or for individuals. We used two-choice playback experiments to determine the mating preference functions of in...

Introduction to Quantitative Genetics (Longman, Essex, ed. 4, 1996). 19. Tadpoles were fed finely ground Tetra-Min fish flakes. The high food ration was typically as much as the tadpoles could consume and was always three times the low food ration. Larval survival, growth rate, length of larval period, and mass at metamorphosis differed significant...

When animals, including humans, communicate, they convey information and express their perceptions of the world. Because different organisms are able to produce and perceive different signals, the animal world contains a diversity of communication systems. Based on the approach laid out in the 1950s by Nobel laureate Nikolaas Tinbergen, this book l...

A gray tree frog (Hyla chrysoscelis) genomic library was constructed and characterized with regard to the incidence and complexity of simple sequence repeat (SSR) loci. The partial genomic library, containing approximately 10,000 clones with an average-sized insert of 350 bp, was screened with six SSR repeat oligonucleotides (AC, AG, ACG, AGC, AAC,...

The selectivity of female phonotactic responses to synthetic advertisement calls was tested in choice situations. Preferences based on differences in the linear rise-time of synthetic pulses depended on intensity and carrier frequency. When the carrier frequency was 1.1 kHz, simulating the low-frequency peak in the advertisement call, females prefe...

In order to test the hypothesis that the forebrain is involved in controlling acoustically guided behaviour, we carried out behavioural studies in combination with brain lesions, neuroanatomical and electrophysiological experiments in males and females of different species of frogs. Whereas the dorsomedial pallium plays no or only a minor role, the...

The evolution of communication requires changes in both signals and the criteria used by receivers to select signals. The question arises: Do changes occur first in signals, first in receivers, or are tight co‐evolutionary changes required in both signals and receivers? In the gray treefrog complex, spectral properties of calls are conserved: in bo...

We studied the relationship between auditory activity in the midbrain and selective phonotaxis in females of the treefrog, Pseudacris crucifer. Gravid females were tested in two-stimulus playback tests using synthetic advertisement calls of different frequencies (2600 versus 2875 Hz; 2800 versus 3500 Hz; 2600 versus 3500 Hz). Tests were conducted w...

The "good genes" hypothesis predicts that mating preferences enable females to select mates of superior genetic quality. The genetic consequences of the preference shown by female gray tree frogs for long-duration calls were evaluated by comparing the performance of maternal half-siblings sired by males with different call durations. Offspring of m...

The main aim of this chapter is to outline techniques for recording and characterizing animal communication signals. Signal analysis provides the basis for assessing the repertoires of individuals and species, and for relating variation in signal structure to variation in other phenotypic attributes of the signaler. Correlations are also usually fo...

Breeding biology and description of the advertisement call of Litoria splendida are presented. Analysis of a call of L. caerulea is also provided and shows that these similar, syntopic species have structurally similar calls and thus presumably show significant acoustic interactions in mixed choruses.

The proper design of mate-choice experiments is critical to detecting and characterizing mating preferences. Female anuran amphibians tested in mate-choice experiments are almost always collected in amplexus (i.e. after they have chosen a mate); it has been assumed that these females are as discriminating as they are before they enter amplexus. Thi...

We assessed the potential for several acoustic properties of the advertisement calls of male gray tree frogs to affect relative mating success by relating patterns of variation in these properties to minimum differences required to elicit female choice. Dynamic properties (pulse number, PN; call rate, CR; and duty cycle, DC, the ratio of call durat...

The proper design of mate-choice experiments is critical to detecting and characterizing mating preferences. Female anuran amphibians tested in mate-choice experiments are almost always collected in amplexus (i.e. after they have chosen a mate); it has been assumed that these females are as discriminating as they are before they enter amplexus. Thi...